????近日來，投資者們被市場搞的普遍有些神經過敏。

????9月22日以來，道瓊斯指數已有3天的下跌幅度超過100點。阿里巴巴（Alibaba）巨型IPO橫空出世，以及這家中國電子商務公司的驚人估值，引發市場或已觸頂的擔憂。

????令人擔憂的是，乏善可陳的基本面似乎遠遠無法支撐股市對未來的爆棚信心。我們正生活在一個創紀錄的企業估值與平庸的利潤增長并存的世界之中。

????為了獲得對現實狀況的最準確認知，不妨關注一個能告訴我們股票何時值得買進、何時被高估的指標：股票風險溢價（ERP）。它被譽為企業融資圣杯。這名稱或許聽起來不那么有吸引力，但要想在股市中長期賺錢，這是你能找到的最實用的衡量指標。

????股票風險溢價是投資者選擇投資股票而不投資債券，因承擔這份額外風險而要求獲得的額外回報。ERP越高，潛在的未來回報也越大。例如，在2009年市場恐慌時期，風險溢價激增，那時買進股票的人獲利頗豐。相比之下，當股票風險溢價低于平均值，未來幾年的股票投資收益可能非常微薄，甚或根本不存在。

????但當前具有迷惑性的是，真實可持續的股票風險溢價被暫時的、不可持續的低利率所掩蓋。但要從這些虛幻的官方數據中挖掘出經調整后真實的股票風險溢價，也并非難事。我們將會看到，這一調整后的數據已發出了警報。

????股票風險溢價就是股票預期回報減去10年期美國國債經通脹調整后的收益率，這是你勇敢投資股票而期待獲得的額外容錯余量或空間。最佳的預期回報指標是經濟學家羅伯特?席勒創造的經周期性調整的市盈率（CAPE）收益率。CAPE是最可信的回報衡量指標，它對可能高度誤導性的暫時利潤波動進行了調整。當前，基于CAPE的收益與股價比率為3.8%。倒過來計算的席勒市盈率為26.3倍。

????因此，當前經通脹調整后的預期股票回報為3.8%。第二步是減去10年期美國國債的實際收益率，從而獲得股票風險溢價。這一長期國債的收益率目前約為2.5%，而通脹為2%左右。因此，實際收益率僅為0.5%。

????由此得出，股票風險溢價為3.8%的預期回報減去0.5%，即3.3%。從歷史標準來看，這個數據還不錯。這對于看漲的人士，即便是那些負責任的看漲人士也是一個令人鼓舞的信號。他們會說，3.8%的預期回報加上2%的通脹，總計達到5.8%，還不夠好嗎，看看10年期美國國債的收益率。那么，為何不買進股票？

????即便是那些樂觀人士也承認利率需要上升。當今，低得令人難以置信的0.5%實際收益率造成了一種幻像，令股票風險溢價虛高。事情總歸會回復常態，想想一旦美聯儲放寬利率，讓利率回歸歷史常態，結果會怎樣？假以時日，實際利率將徘徊在2%附近區間。實際利率從當前的0.5%升至2%，推動10年期美國國債收益率升至4%（即2%的實際收益率加上2%的未來通脹溢價），將會發生什么?

????現在，我們可以重新計算股票風險溢價，剔除人為低利率產生的放大效應。3.8%的預期回報減去未來合理的實際利率2%，得出不那么誘人的股票風險溢價：區區1.8%而已。

????這不足以證明投資股票是明智的。假設投資者仍舊要求較債券有3.3%的息差，以達到他們當前預期獲得的收益。那么，他們將要求獲得的未來回報不是5.8%，而是7.3%（即2%的實際利率加上3.3%的股票風險溢價和2%的通脹。）

????要讓股票風險溢價恢復到有吸引力的水平，需要公司估值大幅下降。席勒市盈率比需要從26.3降至18.9，造成股價大降28%。標準普爾指數在1,425點左右將再度變得有吸引力。關注股票風險溢價，關乎投資中最重要的事情：確保你的風險獲得良好回報。因此，敬請密切跟蹤所有市場指標之王——股票風險溢價。（財富中文網）

????譯者：早稻米

????Investors have come down with a case of the jitters, and for a good reason.

????Since September 22, the Dow has careened through three days of 100 point-plus losses. The gigantic pop in the Alibaba IPO and the Chinese e-commerce phenomenon’s epic valuation have begun to stir fears that we’ve hit a market peak.

????What’s worrying is that prices are displaying far greater faith in the future than the unimpressive fundamentals suggest is warranted. We’re living in a world of record-high corporate valuations and mediocre earnings growth.

????To get the most accurate picture of the situation, let’s examine a metric that tells you when stocks are really a buy, and when they’re overly pricey. It’s called the Equity Risk Premium, or ERP, and it’s been lauded as the Holy Grail of corporate finance. The name may sound wonky, but for making money in stocks in the long-term, it’s the most practical measurement you’ll ever find.

????The Equity Risk Premium is the extra return that investors demand for taking the additional risk of choosing stocks over far safer Treasury bonds. The higher the ERP, the bigger the potential future returns. Risk premiums ballooned, for example, in the panic of 2009, and folks who bought then profited handsomely. By contrast, when the ERP is below average, gains on equities tend to be weak or non-existent in the years to come.

????What’s misleading is that the real, sustainable ERP has been disguised by a temporary phenomenon: unsustainably low interest rates. But it’s no great challenge to unmask an adjusted, realistic ERP from the illusory, official one. And as we’ll see, that slender figure is cause for alarm.

????The ERP is simply the expected return on equities minus the inflation-adjusted yield on 10-year treasuries—that’s the extra cushion, or margin for error, you’d expect for braving equities. The best measure of the expected return is the earnings yield on the CAPE, or Cyclically Adjusted Price-Earnings Ratio, developed by economist Robert Shiller. The CAPE is the most reliable yardstick for returns since it adjusts for temporary, highly misleading swings in profits. Right now, the E/P (earnings to price ratio) on the CAPE stands at 3.8%. That’s the inverse of the Shiller price-to-earnings ratio of 26.3.

????So the expected return on stocks is now 3.8%, adjusted for inflation. The second step consists of subtracting the real rate on the 10-year Treasury to get the ERP. The long bond is now yielding around 2.5%, and inflation is running at around 2%. So the real yield is a mere 0.5%.

????Hence, the ERP is our 3.8% expected return minus 0.5%, or 3.3%. By historical standards, that’s a good figure. It’s an encouraging signal for the bulls, even the responsible ones. They can argue that the expected return of 3.8% plus inflation of 2%, or 5.8% in total, isn’t great, but clocks the yields on the long bond. So why not buy stocks?

????Even the optimists, however, acknowledge that interest rates need to rise. Today, the incredibly low 0.5% real yield has created a mirage in the form of a superficially strong ERP. Things always go back to normal, so consider the results when the Fed unshackles interest rates and lets them swing back to their historic norms. Over time, real rates hover in the 2% range. What will happen when they rise from today’s level of 0.5% to 2%, bringing the yield on the 10-year Treasury bond to 4% (the total of the 2% real yield plus a 2% premium for future inflation)?

????Now, we can re-calculate the ERP to eliminate the funhouse mirror effect of artificially low interest rates. The expected return of 3.8%, minus the reasonable, future real rate of 2%, leaves an under-nourished ERP of just 1.8%.

????That’s not enough to justify investing in stocks. Let’s assume investors still demand a spread over bonds of 3.3 points, matching what they’re supposed to be getting today. Now they’ll require future returns not of 5.8%, but 7.3% (that’s the real rate of 2% plus the ERP of 3.3% plus inflation of 2%).

????Restoring the ERP to attractive levels will require a sharp drop in company valuations. The Shiller PE would need to fall from 26.3 to 18.9, causing stock prices to drop by 28%. The S&P would look alluring again at around 1,425. Watching the ERP is all about what really matters in investing: ensuring you are well paid for risk. So follow the sovereign of all market metrics.